Fire tolerance of perennial grass tussocks in a savanna woodland

Grass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.